// { dg-do assemble } class X // Indentation has been done so to see the similarities. { public: X() {} // { dg-message "note" } referenced below X(X& x) {x.i=7;} // { dg-message "note" } Both functions modify the void bar(X& x) {x.i=7;} // { dg-message "note" } reference parameter x. int i; }; X foo() { X x; return x; } int main() { X x(foo()); // { dg-error "no match" } Compiler doesn't warn about temporary reference. x.bar(foo()); // { dg-error "no match" } The same mistake is warned about in this case. }